Fluorescence is a powerful and versatile method that is widely used in several scientific fields. However, when it comes to analyze the origin of a given fluorescence signal (i.e. calibrating the excitation intensity, the number of emitters and their respective quantum yield), fluorescence spectroscopy is intrinsically limited, as it is unable to separately quantify the excitation intensity from the number of fluorescent emitters. This may cause severe misinterpretation of experimental results as soon as complex systems are used, such as plasmonic metal substrates or scattering media. The range of application is large, from bioassays to microscopy imaging.
We address this issue in a recent Optics Letters publication by monitoring higher-order harmonic fluorescence signals upon harmonic excitation modulation. To our knowledge, this is the very first method able to quantify the excitation intensity and the number of emitters separately. It is a significant supplement to the fluorescence toolbox. The method is compatible with a wide range of observations, and relatively simple to implement. This opens new characterization routes for applications on surface-enhanced fluorescence bioassays, microscopy across scattering samples, and deep tissue fluorescence imaging.
My coworker Heykel Aouani will defend his PhD on September 08th (13:00, Ponte Amphi). The thesis is entitled "Optical nanoantennas to enhance and control molecular fluorescence in subwavelength volumes".
- Prof. Romain Quidant (ICFO Barcelona, reviewer)
- Dr Alexandre Bouhelier (ICB Dijon, reviewer)
- Prof. Xavier Letartre (INL Lyon)
- Prof. Emmanuel Fort (ESPCI Paris)
- Dr. Herve Rigneault (Fresnel Marseille)
- Dr. Jerome Wenger (thesis supervisor)
Abstract: Optical nanoantennas allow manipulation, connement and enhancement of light in subwavelength volumes. The applications of these nano-objects are related to various fields such as nano-light sources, photovoltaic, microscopy, spectroscopy ... The physical properties of these nanoantennas depending mainly on their nature, sizes and geometries, the experimental characterization of these nano-objects is essential because it allows to improve signicantly their design and amplify the electromagnetic responses. The focus of this work concerns the characterization and exploitation properties of optical nanoantennas. Several experimental characterization techniques of nanoantennas have been developed during this thesis : fluorescence correlation spectroscopy FCS, temporal dynamics monitoring of quantum dots, spectroscopy by saturated excitation of fluorescence. These techniques were applied to study different types of optical antennas : dielectric microspheres, bare nanoapertures and corrugated nanoapertures. These optical antennas have been used to effectively improve the detection of fluorescent molecules in solution, with fluorescence enhancement greater than a factor of 100, together with a directivity control of the fluorescence emission, opening new opportunities in biophotonics.